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Session 124 - Elliptical Galaxies.
Oral session, Saturday, January 10

[124.02] On the Origin of the UV Upturn in Elliptical Galaxies


The unexpectedly high UV flux in the spectra of giant elliptical galaxies (UV upturn), has been one of the most controversial topics in current astronomical research. This thesis presents a population synthesis and analysis which concludes that this phenomenon is a natural result of the advanced stellar evolution of a metal-rich population of stars. All three important empirical discoveries about the UV upturn - the fact that strong UV upturns are restricted to giant ellipticals, the positive UV upturn-metallicity relationship, and the narrow range of the T_eff of UV sources - are closely reproduced for reasonable ranges of input parameters. Old, metal-rich populations, such as giant ellipticals, easily develop hot core helium-burning stars (and thus a UV upturn) because, when a positive galactic helium enrichment parameter is assumed, more metal-rich red giants experience higher mass loss at a given age and (2) the UV bright phase of the core helium-burning stars is more prominent in more metal-rich stars. We discuss the major sources of uncertainties in the models, such as the production and role of hot horizontal-branch stars, and the importance of galactic nucleosynthesis.

Program listing for Saturday